What is the recommended treatment for non-pregnant adults with Group B streptococcus (GBS) infections?

Treatment of Group B Streptococcus Infections in Non-Pregnant Adults

For invasive GBS infections in non-pregnant adults, penicillin G remains the preferred first-line treatment due to its narrow spectrum and proven efficacy, though higher doses than those used for Group A streptococci are required. 1, 2

First-Line Treatment Regimens

Penicillin-Based Therapy (Preferred)

• Penicillin G is the drug of choice for invasive GBS disease in non-pregnant adults, administered as 12-24 million units/day IV in divided doses depending on infection severity 1, 2
• For serious infections such as bacteremia or pneumonia: 12-20 million units/day IV in divided doses 1
• For meningitis or endocarditis: 18-24 million units/day IV (administered as 2-4 million units every 4 hours) 1
• Ampicillin is an acceptable alternative: 150-200 mg/kg/day IV in divided doses every 3-4 hours for serious infections 3

Critical Consideration: Higher MICs

• GBS exhibits penicillin MICs that are 4-8 fold higher than Group A streptococci, necessitating higher dosing than might be used for other streptococcal infections 2
• This pharmacologic reality explains why standard penicillin dosing may be inadequate for severe GBS disease 2

Treatment for Penicillin-Allergic Patients

Low-Risk Penicillin Allergy (No Anaphylaxis History)

• Cefazolin is the preferred alternative: 2 g IV initial dose, then 1 g IV every 8 hours 4
• This applies to patients without history of immediate hypersensitivity reactions (anaphylaxis, angioedema, urticaria) or conditions that would make anaphylaxis more dangerous 4

High-Risk Penicillin Allergy (Anaphylaxis Risk)

• Clindamycin 900 mg IV every 8 hours if the isolate is confirmed susceptible through antimicrobial susceptibility testing 4, 5
• Vancomycin 1 g IV every 12 hours if susceptibility testing is unavailable, results are unknown, or the isolate is resistant to clindamycin 4
• Erythromycin is not recommended due to increasing GBS resistance to macrolide antibiotics 4, 6

Important Caveat on Resistance

• Approximately 20% of GBS isolates demonstrate resistance to clindamycin, making susceptibility testing mandatory before using this agent 6
• Resistance to erythromycin and clindamycin has been increasing in recent years across multiple countries 6
• Testing for inducible clindamycin resistance is necessary for isolates susceptible to clindamycin but resistant to erythromycin 7, 8

Infection-Specific Treatment Duration

Common Clinical Presentations

Skin and soft-tissue infections (most common presentation in non-pregnant adults):

• Continue treatment for at least 48-72 hours after clinical improvement 1, 3
• Minimum 10 days total for any GBS infection to prevent complications 4, 3

Bacteremia without focus:

• 10-14 days of IV therapy 9, 2

Endocarditis:

• 4-6 weeks of IV therapy 1, 2

Meningitis:

• 2 weeks minimum of high-dose IV therapy 1

Osteoarticular infections:

• 4-6 weeks of therapy, often requiring surgical debridement 2, 10

High-Risk Populations Requiring Vigilance

• Diabetes mellitus is the most significant underlying risk factor for invasive GBS disease in adults 2, 11, 10
• Elderly patients (average age ~50 years in case series) are at increased risk 11, 10
• Immunocompromised hosts, including those with cancer, cirrhosis, or neurological impairment 2, 11, 10
• Nosocomial infections related to IV catheter placement are common 2

Critical Clinical Pitfalls

Recurrence Risk

• Recurrent infection occurs in 4.3% of survivors, necessitating close follow-up after treatment completion 2
• Consider extended therapy or investigation for underlying immunodeficiency in recurrent cases 2

Antibiotic Resistance Monitoring

• While GBS remains universally susceptible to beta-lactams in most regions, reports of reduced susceptibility to penicillin have emerged in some countries 6
• Resistance to fluoroquinolones and aminoglycosides continues to rise 6
• Two documented cases of vancomycin resistance in GBS have been reported, though vancomycin remains largely effective 6

Inadequate Dosing

• Underdosing or premature discontinuation leads to treatment failure or recurrence 7, 8
• The higher MICs of GBS compared to other streptococci mean that standard "streptococcal" dosing may be insufficient 2

Failure to Obtain Cultures

• Blood cultures should be obtained before initiating therapy to confirm diagnosis and guide treatment 9
• Susceptibility testing is essential for penicillin-allergic patients to guide alternative antibiotic selection 4, 8

Emerging Epidemiology

• GBS disease in non-pregnant adults is increasing, particularly among elderly persons and those with significant underlying diseases 4, 2
• The burden of GBS disease in non-pregnant adults has not been adequately addressed by current prevention strategies focused on perinatal disease 4
• Capsular serotypes Ia, III, and V account for the majority of disease in non-pregnant adults 2